This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to SE 9904632-8 filed in Sweden on Dec. 17, 1999; the entire content of which is hereby incorporated by reference.
The present invention relates to transmission of data in digital mobile communication systems, in particular to a system and a method for non-transparent transmission of data in digital mobile communications system.
In digital mobile communication systems data can be transmitted physically in two different manners, namely transparently and non-transparently. For transparent transmissions, data is transferred transparently over a traffic channel of the mobile communication system which means that error correction on the radio path is performed through the use of channel coding only. For example for the GSM system a channel coding scheme denoted Forward Error Correction (FEC) is used.
For non-transparent transmissions, in addition to channel coding as referred to above, a further protocol is used according to which the data transmission over the traffic channel is repeated if the data was not received correctly at the receiving side. In the GSM system such further communication protocol is denoted Radio Link Protocol (RLP). It is used between terminal adapting means of a mobile station and network adapting means, e.g. an InterWorking Function IWF, which mostly is provided at a Mobile Switching Center MSC, or in association therewith. The RLP is a balanced data transfer protocol of HDLC type which has a frame structure. Error correction by the RLP is based on re-transmission of frames corrupted over the traffic channel. There is also another protocol L2R (Layer 2 Relay) above the RLP. Generally there are functional means both in the mobile station (i.e. in its terminal adapter) and in the Inter Working Function handling such protocol. Data is normally transported in RLP frames over the radio interface between the functional means handling the RLP protocol in the mobile station and in an IWF, respectively. In a normal data transfer state, i.e. for the 9,6 kbps channel that uses 12 kbps on the radio channel, the functional means provides for packing the data into 200-bit PDU:sxe2x80x94(Packet Data units) transferred in 240 bit RLP-frames over the radio interface to another functional means.
So called Discontinuous Transmission (DTX) is advantageously applied when there is no data or other information to be transferred. DTX is a method for reducing transmission on the radio path as much as possible when there is actually no data to be transferred, which means that the transmission is interrupted. The reason for using DTX is to reduce power consumption in the transmitting means, which is of the utmost importance for mobile stations, and also to reduce the overall interference level on the radio path. DTX operates in an independent manner for the uplink and for the downlink, respectively. DTX may be implemented or not in a mobile communications network, i.e. either the network allows DTX or not.
In mobile communication systems implementing TDMA (Time Division Multpile Access) e.g. GSM, each mobile station is assigned one traffic channel for transmission of speech or data. There can thus be maximum eight parallell connections to different mobile stations on one and the same carrier wave for fullrate transmission. Therefore the maximum transfer rate for data is limited to quite a low level due to the available bandwidth, the channel coding and the error correction; thus for the GSM system it is limited to 14.5 kbps, (12 kbps, 6 kbps or 3.6 kbps). However, in e.g. GSM all terrestrial transmission is based on circuit switched transmission.
Through the introduction of GPRS (the packet data service for GSM, General Packet Radio Service), EDGE (Enhanced Data Rates For Global Evolution) and Adaptive Multi Rate (AMR) speech codecs in GSM the bandwidth can be increased and varied. The transmission structure within the Base Station Subsystem (BSS), however, has not been changed in order to be able to take advantage of such development. For private networks or for office solutions, GSM systems are evolving which use the normal LAN (Local Area Network)/Intranet within the company, i.e. IP based transmission is used. However, the QoS issue is not addressed in any other manner than through over-provisioning within an office or with any other QoS mechanisms supported by the computer LAN infrastructure. The bandwidth is also cheap using LAN/Ethernet technologies. However, for public solutions the situation is different and the bandwidth is expensive.
For transmission of non-transparent data within GSM, DTX is supported which means if there is no data to be sent, the radio transmitter can be turned off. In GSM all terrestrial transmission is actually based on circuit switched transmission. Through the introduction of GPRS, the current GSH system is actually upgraded to support packet switched services over the radio interface. Thus a DTX functionality can be used for statistical multiplexing between mobile station and the BTS (Base Transceiver Station), i.e. on the radio path. For the terrestrial transmission packet switching is being defined within the GPRS Core network and the interface (Gb) to BSS (Base Station Subsystem).
In GSM a so called Transcoder and Rate Adaptor Unit, TRAU, which is a transcoder unit that may be arranged apart from the base station, is provided. TRAU communicates with the channel coding unit for example of a BTS which communication is defined in GSM recommendation 08.60. On the uplink direction the BTS always sends the frames received over the radio interface. On the downlink direction the Inter Working Function IWF, which generally is provided in the MSC, which comprises network adapting functionality, indicates whether the frame shall be sent or not by inband signalling within the Radio Link Protocol RLP, frames that are always sent to the BTS via TRAU. As can be seen, much idle data is sent which is a waste of resources.
Through the introduction of High Speed Circuit Switched Data, HSCSD, it gets possible to use several Time Slots (TSs) on the radio interface to one mobile station. Transmission can be transparent as well as non-transparent. For transparent services, the number of TSs are the same on the uplink and on the downlink. For non-transparent transmission there also exists asymmetrical usage of the TSs. The reason therefore is that the typical data services like web-browsing are highly asymmetrical and that the MS implementation faces a threshold in cost if data has to be sent and received at the same time. Therefor most HSCSD MSs will support asymmetrical use of times slots with the relations 1/1, 1/2, 2/2, 1/3, 1/4 meaning one time slot on the uplink, one on the downlink, one on the uplink, two on the downlink etc. Non-transparent services also have the advantage over transparent services that they include the possibility of adaptive radio resource handling. This means that a data user is guaranteed the connection on one time slot and addition thereto can use available radio resources in the cell. The case is similar for GPRS wherein the MS only uses the radio resources when needed. Also here the usage can be asymmetrical. The MS design problems are similar to HSCSD.
To summarize, currently there is no satisfactory solution as to how to provide for an efficient usage of resources, e.g. on the fixed or terrestrial connection between base station and switching arrangement when packet based services are introduced.
What is needed is therefore a communication system supporting communication of data which has a transmission efficiency which is increased as compared to hitherto known systems. Particularly, a system is needed, through which the fixed connection can be used more efficiently for non-transparent data transmission. Further yet a system is needed through which bandwidth can be used efficiently and which is cheap and easy to implement. Moreover, a method for transmission of data in a mobile communication system is needed, through which the above mentioned objects can be fulfilled.
Therefor a mobile communication system supporting communication of data is provided which comprises at least one base station connected to a switching arrangement over a connection and uses a communication protocol for communication between a mobile station and the switching arrangement. The connection between the base station and the switching arrangement supports packet switched communication of data and means are provided for detecting in the base station if data frames sent from the mobile station are correctly received over the air interface. Moreover means are provided for sending only data frames detected as correctly received on to the switching arrangement using the packet switched connection between the base station and the switching arrangement.
Particularly non-transparent communication of data transported as data frames is established on the uplink from the mobile station. Further still the means for detecting in a preferred embodiment comprises means for calculating a frame checksum for a received data frame. In an alternative implementation the quality of the radio transmission is detected in the base station to detect if a data frame is correctly received. This can be done as an alternative to, or, in combination with, the calculation of a frame checksum. In one implementation the switching arrangement is a Mobile Switching Center (MSC).
Alternatively the switching arrangement is a Base Station Controller (BSC), the base station is a Base Transceiver Station (BTS) and packet switched communication of data is supported at least on the uplink between the Base Tranceiver Station (BTS) and the Base Station Controller (BSC).
Particularly the BSC includes transcoding and adapting means for communication with an interworking function of a mobile switching center which comprises means for building frames for transportation of data, the transcoding and adapting means detecting if frames received from the mobile switching center contain data and sending only data frames on to the base station. In an advantageous implementation packet switched communication of data is supported between the base station and the switching arrangement also on the downlink.
The inventive concept is also applicable to a mobile communication system supporting communication of packet data. The system comprises at least one base station connected to a switching arrangement over a connection and a uses communication protocol for communication between the mobile station and the switching arrangement.
The connection between the base station and the switching arrangement supports packet switched communication of data and means are provided for detecting in the base station if data frames sent from the mobile station are correctly received over the air interface. Moreover means are provided for sending only data frames detected as correctly received on to the switching arrangement using the packet switched connection between the base station and the switching arrangement. Advantageously the means for detecting comprises means for calculating a frame chechsum for a received data frame.
Particularly non-transparent communication of packet data is supported and packet switched communication is supported also on the downlink from the switching arrangement to the base station.
According to the present invention it is suggested to introduce packet switched transmission within the BSS in order to increase the flexibility in the transmission efficiency when using statistical multiplexing. It is particularly suggested to use the Internet Protocol (IP). Other alternatives are for example to use ATM (Asynchronous Transfer Mode) or Frame Relay. To introduce Quality of Service (QoS) in an IP network a standard called Differentiated Services is evolving which is based on using priority bits in the IP header. The standard is being standardised by IETF (Internet Engineering Task Force), cf. RFC (Request For Comment) 2475, xe2x80x9cAn architecture for differentiated services.xe2x80x9d However, when packet based transmission is introduced into GSM BSS, it is required that it be possible to meet the current delay requirements of GSM, speech being the most delay sensitive traffic and has to be put in the highest delay priority class. Other services, for which the delay requirements are less strict, will be assigned a lower priority class, e.g. non-transparent data, which have a variable delay by default.
Particularly, for non-transparent data it is allowed for DTX to be used for statistical multiplexing on the fixed connection, which is extremely advantageous. Even more particularly, DTX can be used for statistical multiplexing between the BTS (in GSM) and the TRAU (Transcoder and Rate Adaptor Unit) in BSC. Even more particularly it may be implemented between BTS and MSC. For GPRS the inventive concept can be implemented between BTS and SGSN or BTS and BSC. The TRAU of GSM here corresponds to PCU that may be located either in BSC or SGSN.
To meet the above mentioned objects a method of transmitting data in a mobile communication system is provided. The method comprises the steps of; establishing a non-transparent data connection between a mobile station and a switching arrangement, comprising an air interface between the mobile station and a base station and a packet switched connection between the base station and the switching arrangement; detecting in the base station if data frames sent from the mobile station are correctly received over the air interface; and sending only data frames detected as correctly received on to the switching arrangement using the packet switched connection between the base station and the switching arrangement. In a preferred embodiment the step of detecting comprises using a frame checksum defined in the non-transparent data protocol to establish if the data frames are correctly received.
As an alternative, or an additional, step, the method comprises the step of; performing radio quality measurements in the base station to establish if data frames are correctly received over the air interface from the mobile station. In a particular implementation the method further comprises the step of; detecting in the base station if a received time slot from the mobile station is symmetrical, and, only if the time slot is symmetrical, sending data packets over the packet switched connection to the switching arrangement.
In an advantageous implementation the method includes the step of; implementing packet switched transmission also on the downlink from the switching arrangement to the base station.
The invention concept is also applicable to a mobile communication system supporting communication of packet data. The method then comprises the steps of; establishing a non-transparent data connection between a mobile station and a switching arrangement, comprising an air interface between the mobile station and a base station and a packet switched connection between the base station and the switching arrangement; detecting in the base station if data frames sent from the mobile station are correctly received over the air interface; and sending only data frames detected as correctly received on to the switching arrangement using the packet switched connection between the base station and the switching arrangement.
Particularly the step of detecting comprises using a frame checksum, defined in the non-transparent data protocol, to establish if the data frames are correctly received. Moreover, in an advantageous implementation, the method also comprises the step of; implementing packet switched transmission on the downlink from the switching arrangement to the base station. Substantially the same inventive procedure as described more in detail with reference to the uplink is also implemented for the downlink in advantageous embodiments.
Particularly the inventive concept is applicable to circuit switched data and packet switched data (GPRS), single and multislot, in any combination, and to packet based transmission in the radio access network.
Moreover, the invention also covers all kinds of mapping between radiocarrier (circuit switched (CS) or packet switched (PS) solutions) and core network (CS or PS). This is actually the case for UMTS (Universal Mobile Telephone System) and can also be implemented for GSM/GPRS/EDGE. Thus a circuit switched radio channel can be connected to the packet switched core network of GPRS or a GPRS packet switched radio channel can be connected to a circuit switched carrier of the circuit switched core network of e.g. GSM. What is implemented depends only on the requirements imposed by the implemented service. Thus could e.g. GSM-interfaces A and Gb be migrated to the In-interface of UMTS.
It is an advantage of the invention that the overall flexibility and transmission efficiency is considerably increased.